<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>画板</title>
    <link rel="stylesheet" href="style.css">
</head>

<body>
    <canvas id="canvas" width="100" height="100"></canvas>
    <script>
        let canvas = document.getElementById("canvas");
        canvas.width = document.documentElement.clientWidth
        canvas.height = document.documentElement.clientHeight
        let ctx = canvas.getContext("2d");
        ctx.fillStyle = "black";
        ctx.strokeStyle = 'black'
        ctx.lineWidth = 20;
        ctx.lineCap = 'round';

        function drawLine(x1, y1, x2, y2) {
            ctx.beginPath();
            ctx.moveTo(x1, y1);
            ctx.lineTo(x2, y2);
            ctx.stroke();
        }


        let painting = false
        let last

        var isTouchDevice = 'ontouchstart' in document.documentElement;
        if (isTouchDevice) {
            canvas.ontouchstart = (e) => {
                let x = e.touches[0].clientX
                let y = e.touches[0].clientY
                last = [x, y]
            }
            canvas.ontouchmove = (e) => {
                let x = e.touches[0].clientX
                let y = e.touches[0].clientY
                drawLine(last[0], last[1], x, y)
                last = [x, y]
                // ctx.beginPath();
                // ctx.arc(x, y, 10, 0, 2 * Math.PI);
                // ctx.stroke();
                // ctx.fill();
            }
        } else {
            canvas.onmousedown = (e) => {
                painting = true
                last = [e.clientX, e.clientY]
            }

            canvas.onmousemove = (e) => {
                if (painting === true) {
                    drawLine(last[0], last[1], e.clientX, e.clientY)
                    last = [e.clientX, e.clientY]
                }
            }
        }

        canvas.onmouseup = () => {
            painting = false
        }










    </script>
</body>

</html>